Asked if Jackson would be back at work Monday, his chief of staff, Rick Bryant, told NBC News: "I hope so."

The Mayo Clinic revealed last month that Jackson, the son of civil rights leader and former presidential candidate Jesse Jackson, was being treated for bipolar depression, a condition that affects the parts of the brain controlling emotion, thought and drive.

Millions of people have bipolar disorder. It is marked by highs and lows of mood, and can be treated by medication and psychological counseling, according to the Mayo Clinic's website.

It's not clear when Jackson checked out of the clinic. Doctors there would not give specifics and referred all questions to his congressional office.

Jackson faces a reelection battle this November.

This article includes reporting by NBCChicago.com, Reuters and NBC News' Nadine Comerford. Follow her on Twitter: @NComerfordTV